Advice for recorders of Patella depressa on iNaturalist & (in Britain) iRecord.
[Note that iNaturalist 'Research Grade' records from Britain are automatically passed to iRecord where they are assessed by accredited verifiers before being passed to NBN maps. On the P. depressa map at https://species.nbnatlas.org/species/NHMSYS0021056395 the real distribution is that of the crowded dots. The scattered dots are incorrect. The Marine Recorder of Concholgical Society of GB & Ireland and I are working to get them removed.]
Dear Recorder,
The shell of Patella vulgata is very often as low as on P. depressa, and is very frequently mistaken for it in Britain and Ireland. If yours is a dead, fresh shell, please remove loose debris and position it carefully to take 3 views, as at https://flic.kr/p/2hKbikx . A single exterior view is very unlikely to be sufficient for verification.
Records for P. depressa will only be accepted on iRecord with an image that shows some or all of these features:
1) dark brown/black foot (insufficient alone as P. vulgata sometimes as dark).
2) chalky white, opaque pallial tentacles around periphery (best seen when attached to glass in water, as on left of https://flic.kr/p/2hKbikx )
3) chalky white marks near tips of ribs on interior (may be lost by erosion).
4) apex of shell offset towards anterior (insufficient alone as applies also to P. ulyssiponensis).
5) interior colouring (often helpful, but not always because of wide variation).
Records claimed anywhere in Ireland, or out of area in Britain and northern Europe, as demonstrated by the map and caption at https://flic.kr/p/BewPND , require 1 & 2 for acceptance, as such records would change the understanding of this species. For full details please read the account at https://flic.kr/s/aHskokisge .
Because P. depressa is apparently one of the commonest limpet species in southern Europe there seems to be a tendency on iNaturalist for records of any limpet there to be identified by some recorders as it by default.
P. ullyssiponensis, P. vulgata and P. rustica are all widespread in Galicia. Southwards, they are joined by other limpet-form species, such as Siphonaria pectinata. Many of these may be mistaken for P. depressa when only a single exterior image is shown. In such cases, the generalised suggestion of ‘Patellogastropoda’ is likely (though S. pectinata is not in that subclass).
For Atlantic coasts of Iberia, a useful aid is Trigo et al. 2018. Guia de los Moluscos Marinos de Galicia.
